Chromium-free surface-treated tinplate, production method and surface treating agent therefor

Abstract

Provided are a chromium-free surface-treated tinplate, a production method and a surface treating agent thereof. By coating, on the surface of a tinplate, an environmentally friendly aqueous surface treating agent containing 0.1-5 wt % of a zinc salt, 0.1-5 wt % of a zirconium salt and/or a molybdenum salt and 5-30 wt % of siloxane or polysiloxane, a layer of chromium-free passivation film having uniform and dense ingredients and a good performance and being stable is formed on the surface of a tin layer. The passivation film contains 0.1-20 mg/m2 of zinc, 0.1-20 mg/m2 of zirconium and/or molybdenum and 0.5-100 mg/m2 silicon. The passivation film can impart an excellent surface stability, corrosion resistance and paint film adhesion performance to the surface of the tinplate; in addition, contact with food is safe. The tinplate is comparable to chromium passivation in performance, and the production process thereof does not use a chromate, so that a truly green production process of a tinplate is achieved, complying with the requirements of increasingly strict environmental protection laws and regulations.

The invention claimed is: 
     
       1. A chromium-free surface-treated tinplate, wherein a chromium-free passivation film is formed on a surface of a tin layer, wherein the chromium-free passivation film comprises 0.1-20 mg/m 2  of zinc, 0.1-20 mg/m 2  of zirconium and/or molybdenum, and 0.5-100 mg/m 2  silicon, and wherein the chromium-free passivation film is also fluorine-free and phosphorus-free,
 wherein the zinc in the chromium-free passivation film is from a zinc salt, and the zinc salt is selected from the group consisting of zinc sulfate, zinc acetate, zinc nitrate, zinc gluconate, and zinc methionine; and 
 the silicon in the chromium-free passivation film is from an organosiloxane or polysiloxane, and the organosiloxane or polysiloxane is obtained by hydrolysis of an epoxy silane coupling agent. 
 
     
     
       2. The chromium-free surface-treated tinplate of  claim 1 , wherein the zirconium in the chromium-free passivation film is from a zirconium salt; the molybdenum in the chromium-free passivation film is from a molybdenum salt. 
     
     
       3. The chromium-free surface-treated tinplate of  claim 2 , wherein the zirconium salt is selected from the group consisting of zirconium oxysulfate, zirconium oxynitrate, ammonium zirconium carbonate, tetrabutyl zirconate, and zirconium isopropoxide. 
     
     
       4. The chromium-free surface-treated tinplate of  claim 2 , wherein the molybdenum salt is selected from the group consisting of molybdic acid, ammonium molybdate, sodium molybdate, and potassium molybdate. 
     
     
       5. A method for producing the chromium-free surface-treated tinplate of  claim 1 , comprising:
 a) electrotinning process and soft melting treatment, wherein a phenolsulfonic acid tin plating or methanesulfonic acid tin plating process is used as the electrotinning process, wherein the tin layer is subjected to the soft melting treatment after the phenolsulfonic acid tin plating or methanesulfonic acid tin plating process is finished; 
 b) washing, after the soft melting treatment, a surface of a tinplate by immersing the tinplate in water or spraying water to the surface of the tinplate, and removing redundant water on the surface of the tinplate using a wringing roll; 
 c) coating the surface of the tinplate by spraying or rolling an aqueous surface treating agent, and removing redundant aqueous surface treating agent with a wringing roll, wherein a liquid film of the aqueous surface treating agent is coated uniformly; and 
 d) drying the surface of the tinplate coated with the aqueous surface treating agent in hot air, wherein a temperature of the hot air is controlled between 80-120° C., and a drying time is 0.2-2 seconds, and wherein the aqueous surface treating agent is dried into a film and the chromium-free surface-treated tinplate is obtained. 
 
     
     
       6. The method of  claim 5 , further comprising an immersing step prior to the coating step of step c), wherein the immersing step comprises immersing the tinplate in the aqueous surface treating agent for 0.2-5 seconds. 
     
     
       7. The method of  claim 5 , wherein the aqueous surface treating agent comprises 0.1-5 wt % of the zinc salt, 0.1-5 wt % of the zirconium salt and/or the molybdenum salt, 5-30 wt % of an organosiloxane or polysiloxane and a balance of water, wherein the aqueous surface treating agent has a pH of 3-6, and wherein the zinc salt is selected from the group consisting of the zinc sulfate, zinc acetate, zinc nitrate, zinc gluconate, and zinc methionine, and the organosiloxane or polysiloxane is obtained by the hydrolysis of the epoxy silane coupling agent. 
     
     
       8. The method of  claim 7 , wherein the aqueous surface treating agent further comprises at least one of a reinforcing agent, a wetting agent and an organic acid regulator, wherein the reinforcing agent has a content of 0.1-2 wt %, the wetting agent has a content of 0.1-2 wt %, and the organic acid regulator has a content of 0.1-1 wt %. 
     
     
       9. The method of  claim 8 , wherein the reinforcing agent is polyvinyl alcohol, and the wetting agent is polyethylene glycol. 
     
     
       10. The method of  claim 8 , wherein the organic acid regulator is selected from the group consisting of citric acid, acetic acid, and fumaric acid. 
     
     
       11. The method of  claim 7 , wherein the zirconium salt is selected from the group consisting of zirconium oxysulfate, zirconium oxynitrate, ammonium zirconium carbonate, tetrabutyl zirconate, and zirconium isopropoxide. 
     
     
       12. The method of  claim 7 , wherein the molybdenum salt is selected from the group consisting of molybdic acid, ammonium molybdate, sodium molybdate, and potassium molybdate.